The effects of drought stress and humic acid on some physiological characteristics of roselle (Hibiscus sabdariffa)

To study the effect of humic acid and drought stress on some physiological characteristics of roselle (Hibiscus sabdariffa) an experiment was conducted in the research field of Agricultural Education Centre of Jiroft in 2013. Field experiment was carried out as split plot design with three replications. Water deficit stress as main factor with three levels (A1 = Irrigation after 50، A2 = 100 and A3 = 150 mm evaporation from pan class A) and humic acid was sub plots in four methods of application (B1 = non humic acid، B2 = with irrigation، B3 = with irrigation + once spraying، B4 = with irrigation + twice spraying). Humic acid was used with irrigation at 10kg/ha and for spraying at 250ml/100l. Drought stress had significant effect on chlorophyll a، chlorophyll b، carotenoids، relative humidity content and proline of roselle leaves. Interaction effect of humic acid and drought stress was only significant for total chlorophyll and soluble carbohydrate. Drought stress decreased chlorophyll a (48. 22 percent)، chlorophyll b (32. 77 percent)، carotenoid content (79. 64 percent) and relative humidity (12. 59 percent)، while increased proline content (12. 59 percent). Humic acid increased chlorophyll a، chlorophyll b and carotenoids but reduced proline content (15. 04 percent).